Process and apparatus for the melt extrusion of artificial materials



March 16, 1948. -us 2,437 685 PROCESS AND APPARATUS FOR THE MELT EXTRUSION OF ARTIFICIAL MATERIALS Filed Feb. 15, 1944 Inventor H 2 mm {3 E Atforney;

. @gtent eeif Mar. 13,1943

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PROCESS m APPARATUS FOR THE MELT EXTRUSION OF ARTIFICIAL MATERIALS Henry Dreyfus, London, England; Claude Bonard, administrator of said Henry Dreyfus, deceased, assignor to Celanese Corporation of America, a corporation of Delaware Application February 15, 1944, Serial No. 522,458 In Great Britain January 4, 1943 Section 1, Public Law 690, August 8, 1946, Patent expires January 4, 1983 12 Claims. (Cl. 18-8) This invention relates to the production of artificial materials and particularly to the spinning or extrusion of filaments, films, foils and like materials from molten organic filamentforming compositions.

In the spinning or extrusion of molten organic filament-forming compositions, difliculties can arise from the fact that the melting point of the composition is only slightly below the temperature at which the composition decomposes and from the fact that the composition, whether solid or molten, is a poor conductor of heat. The first of these facts limits the time during which it is permissible for the composition to be exposed to the temperature necessary to melt it while the second makes it difiicult to melt the composition in the limited time available and to avoid locally heating the composition to a temperature above that at which the composition decomposes. Furthermore, the compositions when melted are apt to be very viscous unless heated to such a temperature that they are liable to decompose, and difficulty can be experienced while initiating the spinning operation in priming or filling with the molten composition the pump or like means employed for extrusion.

It has now been found that in the spinning of molten organic filament-forming compositions, the melting of the compositions can be conveniently and efficiently effected'by immersing the composition in a liquid heating medium which thus surrounds the solid composition so that heat is applied to the whole surface thereof and rapid and complete melting of the composition is achieved. If, moreover, the heating liquid is of lower specific gravity than the composition to be melted and extruded, this liquid can very conveniently serve for priming the pump or like extruding means, the composition to be extruded then entering the pump without difilculty.

According to the present invention therefore, in the spinning or otherwise shaping by extrusion of a molten organic filament-forming composition, the composition is fed to the point from which it is extruded through a body of liquid that is inert to the composition and is maintained at a temperature sufiiciently high to melt the composition, so that the composition reaches said point in a molten condition. The liquid is preferably of lower density than the composition, so that the molten composition collects below the heating liquid and can readily be drawn of! and extruded. Moreover the extrusion of the molten composition can readily be initiated by allowing the heating liquid to be extruded in the first in- 2 stance, and then changing over to the extrusion of the filament-forming composition. The extrusion operation can thus be started without difliculty notwithstanding a high degree of viscosity in the molten composition.

The heating liquid employed should naturally be inert to the composition, 1. e. such as to have no deleterious eifect, whether by chemical or physical action, on the composition to be melted or extruded. In particular, the liquid should be stable at the temperatures employed for melting the composition so that it does not decompose and give rise to products which might have an undesirable effect on the composition. As a liquid of lower density than the composition to be extruded, it is generally convenient to employ an organic substance, which may be either liquid or solid at ordinary temperatures but is liquid at the temperature required for melting the material to be extruded. Thus, for example, where temperatures of the order of 200-300 C. are required and where the composition to be extruded has a specific gravity a little over unity, stearyl alcohol or other fatty alcohols containing at least 12 carbon atoms may be employed. Alternatively, hydrocarbons, for example aliphatic hydrocarbons containing a large number of carbon atoms, e. g. 30-40, or mixtures thereof may be used. Thus paraffin wax can be employed.

The heating liquid through which the composition is passed may be contained in a vessel in which provision may be made for an inert atmosphere to be maintained over the surface of the liquid, e. g. by supplying nitrogen under slight pressure to the space in the vessel above the liquid. In order to feed the solid composition through the liquid, a lock or chamber may be provided through which the composition may be dropped, piece by piece, to the surface of the liquid through which it passes by gravity. on sinking through the liquid the composition, or such part of it as may still be solid, is retained by a sieve or grid below the surface of the liquid through which the composition does not pass until it is molten. On passing through the sieve or grid the molten composition forms a reservoir or pool at the bottom of the vessel from which material is drawn for the purpose of spinning or extrusion. Thus the molten composition may be extruded by means of a constant delivery pump whose inlet communicates directly with the bottom of the vessel. Means may be provided to maintain the quantity of molten composition available in the melting vessel by employing the level of the heating liquid as a contrcl. Thus, a float maybe provided on the surface of the heating liquid and the rise and fall of this float may make and break an electrical contact by means of which the pressure lock is operated and pieces of solid composition automatically fed through it. Alternatively, the making or breaking of an electrical contact in this manner may serve to give a visual indication of theamount of composition available, the further supply of solid composition being controlled manually in accordance with such visual indication.

The apparatus is preferably arranged so that the quantity of molten composition available for extrusion at any time is a minimum consistent with the maintenance of a constant supply. In this way, the period during which the composition is exposed to the temperature necessary to melt it is further reduced. For reasons of lightness and economy, it is also desirable that the body of heating liquid should be as small as possible having regard to its function as a reservoir of heat from which heat is drawn to melt the composition employed. If desired, the apparatw may be arranged so that two or more pumps may be fed from a single pool or reservoir of molten composition.

The heating of the heating liquid may be efiected by any convenient means according to the temperature to be maintained and other relevant considerations. Thus, the vessel in which the composition is melted may be enclosed in a jacket containing a heating fluid or it may be surrounded with electrical windings. Or again, the liquid heating medium may be heated in a separate vessel and circulated through the vessel in which the composition is melted or through several such vessels. The whole apparatus is preferably externally lagged so as to prevent loss of heat and discomfort to the operatives.

Control of the heat supplied to the apparatus can be efi'ected by suitable temperature regulating means in accordance with the temperature existing within the apparatus. While it is desirable to supply heat to all parts of the apparatus containing liquid heating medium or molten composition, separate sources of heat under separate temperature controls may be employed for the difierent parts, e. g. one control for the melting vessel and its supply lock and another for the pump and the passage by which molten composition is fed to it. Again, the supply of heat to the melting vessel may be efiected by circulation of heating liquid separately heated, and controlled by controlling the circulation, while heating of the pump and the control of that heating may be eifected electrically,

The invention is applicable generally to the spinning or extrusion of organic filamentdorming compositions that may be spun in the molten state and is particularly advantageous where, as is commonly the case with such compositions, the compositions are liable to'decompose or be otherwise injuriously affected at temperatures not much exceeding those necessary to melt them. Examples of such materials are the synthetic linear superpolyamides made, e. g. by the condensation of diamines with dicarboxylic acids. Or the invention may be applied to compositions having a basis of polyvinyl compound, e. g. polyvinylidene chloride or a copolymer of vinyl chloride with vinyl acetate. Or again, the invention may be applied to compositions having a basis of cellulose derivative such as an organic ester or mixed ester of cellulose, e. g. cellulose acetate,

cellulose propionate or cellulose butyrate, cellulose acetate-butyrate, cellulose acetate-propionate and cellulose acetate-stearate or cellulose ethers such as ethyl and benzyl cellulose.

By way of example, one form of apparatus in accordance with the present invention will now be described in greater detail with reference to the accompanying drawing, which is a sectional side elevation of the apparatus.

The apparatus comprises in general a melt chamber I, a pump chamber 2 and a jet and filter assembly 3. The melt chamber and pump chamber are formed as cavities in a large cast iron vessel 4, the pump chamber 2 being in the form oi a plain cylindrical cavity in the bottom of the vessel and the melt chamber having a cylindrical upper portion and a conical lower portion and being disposed in the upper part of the vessel. The chamber I is closed by means of a heavy cover 5 held down by bolts 6 and sealed by means of a copper sealing ring I.

Passing through a central pressure gland 8 in the cover 5 is a valve rod 9 having a screw portion I and a hand wheel II by means of which it may be raised and lowered so that its lower end I2 may be raised from or engaged with the apex of the conical part of the chamber I, which the end of the rod 9 is formed to fit. The apex of the conical part communicates by way of a passage I4 and connecting pipe I with the pump IS in the pump chamber 2, and this communication may be opened and closed by raising or lowering the valve rod 9. The valve rod 9 is formed with an axial bore in which fits a further valve rod I'I passing into the valve rod 9 through a pressure gland I8 and having a screwed portion I9 and a handwheel 20, by means of which it may be raised and lowered. The lower end 2I of the valve rod I1 is pointed so as to fit on a seating 22 in the bore of the valve rod 9, Just above the seating 22 openings 23 in the wall of the valve rod 9 give access between the bore of the rod 9 and the melt chamber I. A sieve or grid 24 extends across the chamber I near the bottom of the cylindrical portion thereof, being provided with a collar 25 which fits loosely round the valve rod 9 and with a flange 26 which fits the cylindrical portion of the chamber I and rests on the conical portion thereof.

A float 21 is provided in the chamber I from which a contact rod 28 extends upwardly through a guide plug 29, the bore of which is a loose fit round the rod 28. A second contact rod 30 passes through an insulating pressure gland 3I in the cover 5 so that as the float 2! rises and falls contact is made and broken between the rods 28, 30, thereby establishing or breaking an electrical connection between the wires 32, 33, connected respectively to the cover 5 and the contact rod 30.

During the operation of the device the melt chamber I contains a pool of molten composition and a substantial body 35 of the liquid inert to the composition and of lower specific gravity. Pieces of solid composition 3! rest on the grid or sieve 24. The solid composition is introduced into the chamber I by means of a lock generally indicated at 38 comprising two plug valves 39, 40 in series, the plugs having discs 4|, 42 respectively secured thereto whose edges have notches 43 each adapted to engage with the periphery of the other disc. By these means the valves 39 and 40 are interlocked so that neither can be opened unless the other is completely closed. The

valves 39, 40 give access to an oblique passage 44 leading through the cover 8 to the char in order to insert solid composition, the valve 89 is opened (the valve 40 being closedi and a piece of composition is dropped through the aperture :5 and is checked by the valve 40. The valve 39 is then closed and the valve-40 is opened, whereupon the piece oi composition passes through the passage 44 into the chamber l. The opening of the electrical connection between wires 32 and 33 gives an indication that fresh composition is required, and the insertion of fresh composition raises the level of the liquid 38 in the chamber I so as to re-establish the contact until a further supply of fresh composition is required.

Heat is supplied to the melt chamber i by means of heating elements 41 supplied with current through leads 43, the heat so supplied maintaining the liquid 33 at such a temperature as to melt the solid composition 31 at the required rate. The solid composition sinks through the liquid 36 and rests on the grid or sieve 24 and, when molten, passes through the grid to join the pool of molten composition 35.

The spinning operation is started by melting an initial charge of composition, the valve 9 being closed by means of the hand-wheel ll until a sufficient pool 35 of molten composition has accumulated. While the pool 35 is accumulating, the valve I! may be opened so that the liquid 36 may pass through the apertures 23 and through the bore of the valve rod 3 to the passage i4 and thence by way of the pipe I5 to the pump it by which it is forced through a filter 50 and let 5i. When a suificient pool of molten composition 35 has accumulated, the valve I1 is closed (it is in this position that the apparatus is shown) and the valve 8 is opened so that the molten composition passes from the pool 35 through the pump IE to the spinning jet 5|, the pump and jet being already primed by means of the inert liquid 36 which has passed through them;

The action of the pump I6 is assisted by means of an atmosphere of nitrogen maintained in the chamber [above the surface of the liquid 35. This is supplied to the vessel by a supply pipe 58, and an oblique passage 53 similar in form to the passage 44 through which solid composition is supplied to the chamber. If desired the passage l4 may be connected directly to the filter and jet assembly 3, the pump 33 being omitted, and extrusion effected solely by the pressure of the atmosphere of nitrogen above the surface of the liquid 36.

The vessel 4 and the filter and jet assembly 3 are insulated against heat loss by means of a heavy layer 53 of a non-conducting material. The space in the pump chamber 2 surrounding the pump i6 is filled with metal turnings 54 which augment the heat capacity of that part of the vessel 4 surrounding the pump chamber and help to maintain steady the temperature of the molten composition during its passage-from the pool 35 to the spinning jet 5|. In addition, heat may be supplied to the pump chamber 2, and also if desired to the filter and jet assembly 3 by means such as electrical heating elements 55 supplied with current through leads 5.

Having described my invention, what I desire to secure by Letters Patent is:

1. Process for the extrusion of a fusible organic filament-forming composition, said process comprising supplying fused composition to a point from which it is to be extruded by supplying solid composition to a body of heating liquid that is immiscible with and chemically inert to said comiii position, passing said composition through said body of heating liquid to said point and main taining said heating liquid at a temperature sufficiently high to melt the composition in its passage through said heating liquid, and continuously extruding the molten composition, without interruption for the supplying of said solid composition.

2. Process for the extrusion of fusible organic filament-forming compositions comprising supplying fused composition to a point from which it is to be extruded by supplying solid composition from above to a body of heating liquid that is immiscible with, chemically inert to and of lower density than said composition, passing said composition downwards through said body of heating liquid to said point and maintaining said heating liquid at a temperature sufficiently high to melt the composition during its passage through the heating liquid, and continuously extruding the molten composition, without interruption for the supplying of said solid composition.

3. Process for the extrusion of a fusible organic filament-forming composition, said process comprising supplying fused composition to a point from which it is to be extruded by supplying solid composition to a body of heating liquid that is immiscible with and chemically inert to said composition, passing said composition through said body of liquid to said point and maintaining said heating liquid at a temperature sufliciently high to melt the composition in its passage through said heating liquid, straining said composition in its passage through said heating liquid so as to prevent the passage of solid composition to said point and continuously extruding the molten composition, without interruption for the supplying of said solid composition.

4. Process for the extrusion of fusible organic filament-forming compositions comprising supplying fused composition to a point from which it is to be extruded by supplying solid composition from above to a body of heating liquid that is immiscible with, chemically inert to and of lower density than said composition, passing said composition downwards through said body of heating liquid to said point and maintaining said body of heating liquid at a temperature sufllciently high to melt the composition during its passage through the heating liquid, straining the composition in its passage through said heating liquid so as to prevent the passage of solid composition to said point and continuously extruding the molten composition, without interruption for the supplying of said solid composition.

5. Process for the extrusion of fusible organic filament-forming compositions comprising supplying iised composition to a point from which it is to be extruded by supplying solid composition from above to a body of heating liquid that is immiscible with, chemically inert to and of lower density than said composition, passing said composition downwards through said body of heating liquid to said point and maintaining said body of heating liquid at a temperature sufllciently high to melt the composition during its passage through the heating liquid, maintaining over the surface of said body of heating liquid a gas that is under pressure and is chemically inert to said liquid and to the composition, and continuously extruding the molten composition, without interruption for the supplying of said solid composition.

6. Process for the extrusion of fusible organic filament forming compositions comprising supplying fused composition to a point from which it is to be extruded by supplying solid composition from above to a body of heating liquid that is immiscible with, chemically inert to and of lower density than said composition, assing said composition downwards through said body of heating liquid tosaid point and maintaining said body of heating liquid at a temperature sufficiently high to melt the composition. during its passage through the heating liquid, maintaining over the surface of said body of heating liquid a gas that isunder pressure and is chemically inert to said liquid and to the composition, straining the composition in its passage through said liquid so as to prevent the passage of solid composition to said point, and continuously extruding the molten composition, without interruption for the supplying of said solid composition. 1 7. Process for the extrusion of fusible organic filament-forming compositions comprising sup plying fused composition to a point from which it is to be extruded by supplying solid composition from above to a body of heating liquid that is immiscible with, chemically inert to and of lower density than said composition, passing said composition through said body of heating liquid to said point and maintaining said body of heating li uid at a temperature sufficiently high to melt the composition during its passage through the heating liquid, continuously extruding the molten composition without interruption for the supplying of said solid composition, and controlling the feeding of said composition in accordance with the level of the surface of said body of heating liquid so as to maintain said level substantially constant.

8. Process for the extrusion of fusible organic filament-forming compositions comprising supplying fused composition to a point from 'which it is to beextruded by feeding composition downwards to said point through a body of a fatty alcohol containing at least 12 carbon atoms, passing said composition downwards through said body of fatty alcohol to said point and maintaining said fatty alcohol at a temperature sumciently high to melt the composition through its passage through said fatty alcohol, and continuously extruding the molten composition, without interruption for the supplying of said solid composition.

through said wax, maintaining over the surface of said body of wax a gas that is under pressure and is chemically inert to said wax and to the composition, straining the composition in its passage through said wax so as to prevent the passage of solid composition to said point, extruding the molten composition and controlling the feeding of said composition in accordance with the level of the surface of said wax so as to maintain said level substantially constant.

11. Apparatus for the melting and extrusion of fusible organic filament-forming compositions, said apparatus comprising a melting vessel, a body of heating liquid in said vessel that is immiscible with, chemically inert to and of lower density than the composition, said vessel having a lower outlet for the withdrawal of melted composition and an upper outlet for the withdrawal of heating liquid, means for supplying gas under pressure to the top of said vessel, means for heating said body of liquid, means for feeding the composition through said liquid to said lower outlet, a perforated grid extending across'said vessel-below the liquid level therein and in the path of composition to said lower outlet, means operable from outside said vessel for closing said lower outlet to the passing of molten composition during the melting of an initial charge of composition, means for closing said upper outlet for the passing of said heating liquid while said lower outlet is open to the passing of said molten composition, and means communicating with both said outlets for withdrawing liquid material therethrough and extruding said material.

12. Apparatus for the melting and extrusion of fusible organic filament-forming composihaving at the bottom thereof a lower outlet for 9. Process for the extrusion of fusible organic filament-forming compositions comprising supplying fused composition to a point from which it is to be extruded by feeding composition downwards to said oint through a body of molten paraflin wax, passing said composition downwards through said wax to said point and maintaining said wax at a temperature sufliciently high to melt the composition through its passage through said wax, and continuously extrudin the molten composition, without interruption for the supplying of said solid composition.

10. Process for the extrusion of fusible organic filament-forming compositions comprising supplying fused composition to a point from which it is to be extruded by feeding composition downwards to said point through a body of molten paraflin wax, passing said composition downwards through said wax to said point and maintaining said wax at a temperature sufficiently high to melt the composition during its passage the withdrawal of molten composition and, at a point above said lower outlet, an upper outlet for the \mthdrawal of said heating liquid, means for heating said body of liquid, a perforated grid extending across said vessel below the level of said liquid, mean-s for feeding the composition downwards through said body of liquid and through said grid to said lower outlet, means operable from outside said vessel for closing 'said lower outlet to the passage of molten composition during the melting of an initial charge of composition, means for closing said upper outlet while said lower outlet is open, and means communicating with both said outlets for withdrawing liquid material therethrough and extruding said material.

HENRY DREYFUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,769,173 Brannen July 1, 1930 2,133,236 Slayter et al. Oct. 11, 1938 2,278,875 Graves Apr. 7, 1942 2,289,774 Graves July 14, 1942 2,303,338 Dreyfus et al. Dec. 1, 1942 2,303,339 Dreyfus Dec. 1, 1942 2,303,340 Dreyfus Dec. 1, 1942 

